Biometrics authentication refers to methods for identifying a person using an identification target of the living body of the person. Blood vessels of a finger are one identification target of a living body.
For example, an authentication apparatus that generates a three-dimensional image by combining images of different surfaces of a fingertip and that uses this as an identification target has been proposed (for example, see Patent Document 1).
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2002-175529
Meanwhile, a method called a view-volume intersection method (Shape From Silhouette method) exists as one method for generating a three-dimensional volume of an object. In the view-volume intersection method, in accordance with images of an object that were picked up from multiple viewpoints, information concerning a position of a camera, and so forth, when projection from positions of the viewpoints, from which the images were picked up, into a three-dimensional space, which is divided into voxels as units, is performed for the object that is shown in the images, voxels of common portions of projected regions that are projected in the three-dimensional space are obtained as a three-dimensional volume.
There is a case in which surfaces of such a three-dimensional volume are extracted as one of parameters representing the shape of the object or as information that is used to obtain the parameter. As an extraction method in this case, typically, the following method is provided: each of voxels of a three-dimensional volume is considered as a consideration target; and when, among voxels that are in contact with the voxel which is a consideration target, even one voxel that does not constitute the three-dimensional volume exists, the voxel that is a consideration target is extracted as a voxel of a surface of the three-dimensional volume.
Accordingly, for example, as illustrated in FIG. 1, regarding voxels (voxels shaded with diagonal lines in the figure) that correspond to boundaries between voxels of a three-dimensional volume and voxels other than those of the three-dimensional volume (white voxels in the figure), when the voxels are considered as consideration targets, one or more voxels that do not constitute the three-dimensional volume exist. Thus, the voxels are extracted as voxels of surfaces of the three-dimensional volume. Note that, for the sake of convenience, FIG. 1 illustrates a certain cross section of a certain three-dimensional volume.
However, in the extraction method, because of noise or the like, for example, as illustrated in FIG. 2, when a three-dimensional volume having voxels X, which do not constitute the three-dimensional volume, as portions of the inside of the three-dimensional volume is structured, voxels around the voxels X are falsely detected as voxels of surfaces of the three-dimensional volume (the voxels that are falsely detected being illustrated by being shaded with dots in the figure). As a result, there is a problem that extraction accuracy is reduced. Note that, for the sake of convenience, FIG. 2 illustrates a certain cross section of the three-dimensional volume as in the case of FIG. 1.